The invention relates to a control device of an electromagnet comprising a movable core, with at least one inrush phase during which the electromagnet receives an inrush current, and a holding phase during which it receives a holding current weaker than the inrush current, the device comprising at least one coil connected in series with an electronic switch to the terminals of a supply voltage, means for measuring the current flowing in the coil and means for control of the electromagnet, connected to the means for measuring the current and to a control electrode of the electronic switch and comprising means for regulating the current in the coil during the holding phase.
For control of an electromagnet, it is known (FR-A-2,133,652) to supply it temporarily with a relatively high inrush current, followed by a lower holding current. This can be achieved either with a device comprising a single coil, in which the current is switched to constitute the holding current, or with a double coil formed by an inrush coil and a holding coil. It is also known to regulate the inrush and holding currents to preset levels (FR-A-2,568,715).
An electromagnet conventionally comprises a movable core, movement of which to a position in which the electromagnet is actuated is caused by the flow of the inrush current in the inrush coil. It is then held in this position by the flow of the holding current in the holding coil, which may be the same as the inrush coil. To reduce the temperature rise of electromagnets the holding current is sought to be decreased. In certain cases, this decrease of the holding current gives rise to problems due to the existence of shocks, in particular mechanical shocks, liable to cause an unscheduled movement of the movable core to the rest position of the electromagnet.
This type of problem occurs in particular in contactors or in electrical auxiliaries of circuit breakers, for example with circuit breaker opening electromagnets (under-voltage MN or shunt MX) or closing electromagnets (XF).
In a more general manner, seeking to reduce the volumes of the electromagnets leads to a decrease of the power able to be dissipated by the coils and makes the electromagnets more sensitive to shocks.